The copies of the genes for S25 and S17 rRNA in the Tetrahymena macronucleus have been shown to be extrachromosomal and are amplified from one or a few copies which are contained in the germinal micronucleus. The timing and mechanism by which this amplification occurs will be studied during the sexual cycle (conjugation) of this organism. Using a starvation-refeeding regimen after which the only nuclear DNA synthesized is rDNA, the histones which are synthesized concomitantly with rDNA will be analyzed. Using this method to selectively label rDNA, attempts will be made to isolate and to purify the rDNA-containing chromatin to allow detailed analysis of its protein components during different states of activity of the genes for rRNA. Since only one or a few copies of the gene for rRNA in Tetrahymena has been shown to be genetically transmitted while the somatic (macro-) nucleus contains about 200 copies of this gene/haploid DNA amount, we shall examine the number of copies of other genes such as those for S5 rRNA, tRNA and histone mRNA to determine evolution of all repeated genes in Tetrahymena.